Singlet oxygen has heretofore been studied intensively. See, for example, "Singlet Molecular Oxygen" edited by A. P. Schaap, (Dowden, Hutchinson and Ross), 1976; and "International Conference on Singlet Molecular Oxygen and Its Role in Environmental Sciences," Annals of the New York Academy of Sciences, Vol. 171, Act. I, pages 1-302 (1970).
In addition to use in scientific or research-related fields, singlet oxygen has been proposed for a number of applications. For example, singlet oxygen chemically pumps iodine gas lasers. Applications of the latter and other types, however, require substantial volumes and concentrations of singlet oxygen.
Convenient and efficient production of singlet oxygen remains a goal of the art. Although certain solvent-based reactions generate significant amounts of singlet oxygen, such processes possess a number of inherent limitations. The liquid solvent, as well as cryogenic traps and the like for removal of coincidentally produced impurities, tend to quench the singlet oxygen as the latter is produced and consequently limit efficiency of these generators. Moreover, since the by-products of these solvent-based reactions are not regenerated into the initial reactants, the utility of these systems is further compromised. Furthermore, use of the aforementioned solvent based reactions can be hazardous and require massive apparatus.
It has been recognized that irradiation of gaseous ground state oxygen with laser, microwave or other electromagnetic radiation converts ground state oxygen to singlet oxygen. Singlet oxygen has also been generated by irradiating solid-phase dye sensitizer crystals of rose bengal, eosin or methylene blue, for example. Nechers et al, U.S. Pat. No. 4,315,998, proposes chemically binding the photosentisizing catalysts onto a polymer base. But these techniques do not generate singlet oxygen in desired quantities and at sufficient rates.
Schaap et al, U.S. Pat. No. 4,436,715, describes a method for chemical storage of singlet oxygen in an endoperoxide molecular dispersion bound to a solid phase substrate, and for releasing the singlet oxygen so stored by subjecting the endoperoxide to irradiation. The substrate having a dispersion of hydrocarbon acceptor molecules chemically bound thereto may be retrieved and oxidized to form a closed cycle for storage of singlet oxygen in solid phase and retrieval of singlet oxygen in gas phase.